1. Field of the Invention
The present invention relates to a light-quantity control apparatus having at least one of an aperture stop function and a shutter function. The light-quantity control apparatus is installed in an optical apparatus such as a digital camera, a video camera and an interchangeable lens.
2. Description of the Related Art
An optical apparatus such as a camera is necessary to have compactness. In particular, when a lens barrel for holding an image capturing lens protrudes from a camera body in its optical axis direction, it is necessary to reduce a length of the lens barrel in the optical axis direction as short as possible. Japanese Patent Laid-Open No. 2007-310412 discloses a camera having a so-called retractable lens barrel that protrudes from a camera body during a camera use time (image capturing) and is housed (retracted) to the camera body during a camera non-use time (carrying). In this camera, an aperture stop serving as the light-quantity control apparatus and a lens are arranged adjacently to each other in an optical axis direction. Therefore, the length of the lens barrel in the retracted state is reduced by inserting a part of the lenses into the aperture in the retracted state.
Japanese Patent Laid-Open No. 2004-184486 discloses a light-quantity control apparatus in which a plurality of stop blades for controlling a quantity of light by controlling a size of a light-passing aperture (stop aperture) and a driving ring for opening/closing the stop blades are arranged between a base plate and a partition plate, and in which a shutter blade for opening/closing the light-passing aperture (shutter aperture) is arranged between the partition plate and a cover plate. In this apparatus, a cam boss portion provided in the stop blade engages with a cam groove portion formed in the driving ring, and the stop blade is opened and closed by rotation of the driving ring around the light-passing aperture with respect to the base plate. In addition, the shutter blade is opened and closed by a motor installed to the base plate. In this manner, a light-quantity control apparatus having an aperture stop function and a shutter function is implemented using a single base plate. Therefore, a camera can be miniaturized in an optical axis direction, compared to a case where the aperture stop apparatus and the shutter apparatus are separately provided.
However, in the camera disclosed in Japanese Patent Laid-Open No. 2007-310412, part of the lenses are inserted into the aperture formed by opening the stop blade wider than its opened state. For this reason, it is necessary to enlarge a fully opened aperture diameter to be larger than, at least, an outer diameter of the lens. As a result, it is necessary to enlarge the stop blade used to form the stop aperture. In addition, it is also necessary to prepare an outer circumferential space for retracting the stop blade when the stop blade is opened wider than its opened state. Therefore, a size of the light-quantity control apparatus increases in its radial direction. In addition, in the light-quantity control apparatus disclosed in Japanese Patent Laid-Open No. 2004-184486, it is also necessary to provide a thickness of the base plate in the optical axis direction, a space for moving the stop blade, and a space for moving the shutter blade. Therefore, miniaturization is restricted.
In this regard, in the shutter apparatus disclosed in Japanese Patent Laid-Open No. 2-153334, two shutter blades are formed in a curved (spherical) shape, and the shutter blades are moved in their open and close direction along a concave space (hemispherical space) facing their concave surface. In this configuration, it is possible to reduce an outer circumferential space for retracting the shutter blades in a shutter fully opened state, compared to a case where each shutter blade is formed in a planar shape. Therefore, it is possible to miniaturize the shutter apparatus in its radial direction. Such a configuration can be applied to a light-quantity control apparatus for opening and closing a plurality of stop blades. In the configuration employing spherical surface shaped stop blades, it is possible to insert a lens into an concave space formed inside the stop blades or place a concave surface of the lens along convex surface of the stop blades, even when the stop blades are closed (for example, refer to Japanese Patent Laid-Open No. 2007-94074). Therefore, it is possible to reduce a thickness in the optical axis direction when the retractable lens barrel in which the light-quantity control apparatus and the lens are adjacently arranged is retracted.